Collector for barrier grid storage tube



Feb. 1966 M. F. TOOHIG ETAL 3,234,422

COLLECTOR FOR BARRIER GRID STORAGE TUBE Filed July 3, 1961 W Vv k @7 2, A l l M/K INVENTORS. MICHAEL TooH/c;

R. L. DAY

ATTORNEY United States Patent COLLECTOR FOR BER GRID STORAGE TUBE Michael F. Toohig, Fort Wayne, and Cyril L. Day, Huntington, Ind., assignors to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland Filed July 3, 1961, Ser. No. 121,599 12 Claims. (Cl. 313-68) The present invention relates to barrier grid storage tubes and more particularly to the secondary emission collector electrode assemblies incorporated in such tubes. Barrier grid storage tubes are commonly used in such devices as computers, being employed in binary computers for data storage and in a number of radar applications for information storage and/or processing. These tubes are well-known in the art, as shown for example in US. Patent 2,503,949 of April 23, 1948 to A. S. Jensen, et al. Such tubes conventionally include an electron gun assembly including a cathode heated by a suitable filament, a control grid and an accelerating anode, positioned within an elongated envelope at one end thereof. Suitable deflecting and focusing elements are conventionally provided for causing the electron beam produced by the electron gun to scan a target electrode assembly positioned within the envelope at the other end thereof. The target electrode assembly comprises a grid or screen arranged on one side of a dielectric sheet and a metal plate arranged on the other.

If a pattern of repetitive signals is applied to the metallic target substrate in synchronism with the scanning electron beam, no signal will appear at the output of the tube after a few cycles. If a moving signal is present 'in this pattern of repetitive signals (i.e., the background pattern) only the moving signal will appear in the output. The tube can be used in radar MTI or infrared applications where it is desirable to cancel out background radiation and observe only the moving targets.

In aperation an input signal is often applied to the metal plate of the target assembly (the backplate). The

electron beam from the electron gun is caused to scan the dielectric sheet, providing secondary emission greater than unity. Each area of the target electrode formed by the screen or grid forms, in essence, a separate capacit-or with the metal backing plate and thus may be charged positively or negatively by the electron beam depending on the polarity of the input signal applied to the metal plate and screen of the target assembly. These charges may subsequently be taken off the target electrode assem bly by a subsequent scanning by the electron beam. The barrier grid tube further includes a collector electrode and an associated electron optical system for focusing the signal electrons from the target onto the collector electrode, the collector electrode and the electron optical system being normally positioned between the gun and the target.

The output signal from the barrier grid tube may be obtained from the target electrode, but it is preferable to obtain the output signal from the collector electrode. The collector is maintained at a positive potentialwith respect to the target, and the secondary electrons produced'hy the electron beam on the storage surface are directed. toward the collector electrode, from which an output signal is obtained.

One of the disadvantages of barrier grid tube operation is the relativelyhigh backplate-to-collector capacitance. High frequency components of the input signal applied to the backplate are thereby capacitively coupled to the collector. These capacitively coupled signals may be greater in strength than the residual signal from the target in the cancellation mode and thus limit the operation of the tube in this mode.

An object of the present invention is to provide animproved collector for a barrier grid tube particularly one wherein backplate-to-collector capacitance is minimized and an additional stage of signal amplification is obtained.

According to the present invention an improved collector is provided wherein a collector ring is enclosed within a suitable chamber and is shielded from the rest of the tube electrodes in a specific instance by awire mesh.

The present invention is explained with reference to the drawings in which:

FIG. 1 is a cross-sectional view'of a barrier grid storage tube incorporating one embodiment of an improved collector electrode following the principles of the present invention; and I FIG. 2 is a detailed view of another embodiment of a collector electrode following the principles of the present invention.

Referring to FIG. 1, there is shown in schematic form with non-essential details eliminated, a barrier grid storage tube generally identified as 1. The tube includes an elongated envelope 2 having an electron gun assembly 3 positioned therein adjacent end 4. The electron gun assembly 3 may be any conventional type, as is well known in the art, including a cathode heated by a suitable filament, a control grid, and suitable accelerating anodes. The cathode, filament, control grid and accelerating elements are connected to suitable sources of voltage by leads 5, as is well known in the art. The electron beam 6 produced by the electron gun assembly 3 may be deflected vertically and horizontally by suitable deflecting electrodes 7 positioned within the envelope 2 and connected to suitable deflecting circuits by conductors 8 and 9, it being understood that the vertical and horizontal deflection of the electron beam may be provided by deflecting coils arranged on the exterior of the envelope 2 rather than by internal deflecting elements 7. A shield electrode 10 is positioned within the envelope 2 and is connected to a suitable source of potential, for example l00 volts, by lead 11. A novel secondary emission collecting electrode 12 is positioned within envelope 2 in front of shield electrode 1t and is adapted to be connected to a suitable external source of voltageby lead 13. Secondary emission collecting electrode 12 will be discussed more fully hereinbelow. Secondary emission accelerating electrodes 14 and 15 are located between collecting electrode 12 and a target electrode 16 and are adapted respectively to be connected to suitable external sources of voltage by leads 17 and 18. The target electrode 16 is preferably spherical shaped and includes spherical metal backing plate 19 and spherical dielectric and grid elements generally identified as 20 disposed on the side of the metal backing. plate 19 toward the electronic gun assembly 3 for scanning by electron beam 6. The metal backing plate 19 of the target electrode 16 is adapted to be connected to a suitable source of input voltage by lead 21, for example, video input signals.

The operating principles of the barrier grid tube are well known and it is felt unnecessary to restate them in detail. In brief, an input signal is applied via conductor 21 to backing plate 19. An electron beam 6 from electron gun 3 is scanned across dielectric and grid 29 by means of deflecting elements 7. As the dielectric surface is scanned by the electron beam, secondary electrons are emitted and drawn away toward collector electrode 12 which is maintained, during tube operation, at a high positive potential relative to the potential of dielectric 26. Since the secondary electrons from the dielectric surface are emitted in all directions at relatively low velocity, electrodes 14 and 15, maintained during tube operation at different potentials, are used to form a focusing electrostatic field for directing the secondary emission toward the collector electrode 12. The degree of secondary emission is a function of the input signal applied to the backing plate through input conductor 21, thus the output signal from collector electrode 12 will be a function of the input signal applied to conductor 21.

Referring to the secondary emission collector electrode 12 in more detail, it is seen that it is located intermediate shield electrode 143 and accelerating electrode 14. In FIG. 1 collector 12 is an annular structure, the wall of which is colinear with the other electrodes except that a major portion of the wall 120 is formed in the general shape of an open-sided toroid. This is the collector dynode. A collector ring 121; is located within the chamber formed by wall 12a at approximately the center of the circular cross section of the toroid. The collector Wall 12a is biased at approximately 100 to 350 volts above the potential of the barrier grid assembly 20 by a potential source connected to lead 13. Collector ring 12b is biased approximately 50 to 100 volts above the potential of Wall 12a by a suitable potential source connected to lead 12d. A fine mesh screen 120 is mounted across an opening in the collector wall of the inside diameter of the toroid such that the mesh separates the interior of the toroid from the interior of the storage tube. The secondary electrons emitted from the target electrode 16 are electronically focused and accelerated by electrodes 14 and 15, and are attracted to collector electrode 12. The velocity of the secondary electrons carry them into the toroid through mesh 12c and past collector ring 1212 until they strike the inner surface of wall 12a, which is constructed of a highly emissive material, for example beryllium-copper or silver-magnesium. The secondary electrons, in striking the inner surface of wall 12a release further electrons, herein referred to as tertiary electrons, which are attracted to, and are collected by collector ring 12b.

The tertiary electrons collected by collector ring 1212 are a function of the information originally written on the target electrode, and may be removed as an output signal from ring 12b by suitable output means such as conductive lead 12a. The fact that the secondary electrons from the target electrode are not directly collected by ring 1211, but instead release a proportional number of tertiary electrons from highly emissive wall 12a, provides a stage of signal amplification which increases signal detectability and decreases the design requirements of any output preamplifier which may be used. Thus, it is also possible to provide a selected value range for the output signal by selecting an appropriate material for the toroid surface.

The mesh 12c which extends across the toroid opening is preferably composed of tungsten wires and is approximately 92 percent transparent. The mesh serves to eliminate the undesired capacitive coupling between the target electrode and the collector electrode, and also shields the collector ring from the high frequency signals present on backplate 19 during the writing mode.

The collector wall 12a need not necessarily be in the form of an open-sided toroid, but may describe other forms for example wall 12a may form an isosceles triangle with mesh 126, as shown by wall 122 in FIG. 2. Both the curved wall 12:: of FIG. 1 and the angular wall 12a of FIG. 2, when struck by secondary electrons passing through mesh 12c, will emit tertiary electrons in a direction toward collector ring 12b.

It is seen from the above discussion that a unique collector for a storage tube has been devised which eliminates the undesired backplate to collector capacitance, and provides an amplification stage for the collector output signal. It is to be understood that while two specific configurations have been shown for the collector wall, many more suitable shapes may be designed using the principles of the present invention.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim: r

1. In a barrier grid storage tube comprising a first electron beam source, an electron emissive target electrode, means for scanning said beam across said target electrode and means applying a varying input signal thereto for storing a charge pattern thereon, said beam causing emission of secondary electrons from said target electrode in accordance with said charge pattern and input signal, a collector electrode structure positioned to collect secondary electrons from said barrier grid, said collector having an electron emissive surface for emitting further electrons in response to said secondary electrons directed thereon, an output electrode adjacent said surface for collecting said further electrons, and an electron permeable electrostatic shielding means for passing said secondary electrons to said surface while electrostatically shielding said surface and output electrode from the remainder of said tube.

2. In a barrier grid storage tube, a collector electrode structure for collecting secondary electrons from said barrier grid comprising an annular inner wall having an electron emissive surface for emitting further electrons in response to said secondary electrons directed thereon, an inner concentric output electrode for collecting said further electrons and producing an output signal characteristic thereof, and a mesh enclosing said wall and output electrode for passing said secondary electrons to said wall while electrostatically shielding said wall and output electrode from the remainder of said tube.

3. A collector electrode structure according to claim 2 wherein said emissive surface on said wall is berylliumcopper.

4. A collector electrode structure according toclaim 2 wherein said emissive surface on said wall is silver-magnesium.

' 5. A collector electrode structure according to claim 2 wherein said mesh is composed of finely spaced tungsten wires.

6. A collector electrode structure according to claim 2 wherein said Wall is in the shape of a toroid having an open inner side.

7. A collector electrode structure according to claim 6 wherein said mesh is mounted across said open side of said toroid.

8. A collector electrode structure according to claim 7 wherein said output electrode is a ring mounted within said toroid.

9. A collector electrode structure according to claim 2 wherein said wall is in the shape of an annular angle having an inner open side.

10. A collector electrode structure according to claim 9 wherein said mesh is mounted across the open side of said angle.

11. A collector electrode structure according to claim 9 wherein said output electrode is a ring mounted within said annular angle.

12. In a storage tube of the type having a target elcctrode wherein secondary electrons characteristic of information stored therein are periodically released, a ring shaped collector electrode structure comprising an inner wall having an annular depressed surface and an electron emissive coating on said surface for emitting tertiary electrons in response to said secondary electrons directed thereon, accelerating and focusing electrodes directing said secondary electrons to said collector electrode, a concentric output electrode mounted within said depression to collect said tertiary electrons and produce an output signal characteristic thereof, an output conductor coupled to said output electrode, and a mesh enclosing said depression to pass said secondary electrons to said surface while electrostatically shielding said surface and output electrode from the remainder of said storage tube.

References Cited by the Examiner UNITED STATES PATENTS Schlesinger 313--105 Snyder 313-68 Snyder et a1. 31368 Palluel 313105 Jensen 313-68 X Day 313--68 X 10 GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

1. IN A BARRIER GRID STORAGE TUBE COMPRISING A FIRST ELECTRON BEAM SOURCE, AN ELECTRON EMISSIVE TARGET ELECTRODE, MEANS FOR SCANNING SAID BEAM ACROSS SAID TARGET ELECTRODE AND MEANS APPLYING A VARYING INPUT SIGNAL THERETO FOR STORING A CHARGE PATTERN THEREON, SAID BEAM CAUSING EMISSION OF SECONDARY ELECTRONS FROM SAID TARGET ELECTRODE IN ACCORDANCE WITH SAID CHARGE POSITIONED TO COLLECT SECONDCOLLECTOR ELECTRODE STRUCTURE POSITIONED TO COLLECT SECONDARY ELECTRONS FROM SAID BARRIER GRID, SAID COLLECTOR HAVING AN ELECTRON EMISSIVE SURFACE FOR EMITTING FURTHER ELECTRONS IN RESPONSE TO SAID SECONDARY ELECTRONS DIRECTED THEREON, AN OUTPUT ELECTRODE ADJACENT SAID SURFACE FOR COLLECTING SAID FURTHER ELECTRONS, AND AN ELECTRON PERME- 